The present invention relates to a solid silicone defoaming agent.
Silicone defoaming agents are widely used in the art for defoaming and foam suppression. Addition in small quantities to an aqueous or nonaqueous foaming system has a remarkable defoaming effect. The compounds are chemically inert and colorless, transparent, and odorless, and do not have adverse effects.
Foam inhibition is achieved in nonaqueous foaming systems mainly by the use of a defoaming agent comprising a dimethylpolysiloxane silicone oil or a defoaming agent comprising a silicone oil compound in which microparticulate silica is dispersed in dimethylpolysiloxane oil. For defoaming or foam inhibition in aqueous foaming systems, use is made of an emulsion-type defoaming agent in which the silicone oil compound has been emulsified using a suitable emulsifying agent.
However, the prior emulsion-type defoaming agents used for aqueous foaming systems suffer from problems such as poor emulsion stability, resulting in destruction of the emulsion and separation of the silicone oil compound due to temperature changes and shaking during transport, or simply by long-term storage.
Other disadvantages relate to decomposition and the appearance of mold when a suitable preservative or antimold is not added. Further, the defoaming agent is a liquid, so addition to the foaming system necessitates a dosing pump or manual intervention.
A solid silicone defoaming agent has been obtained by melting a water-soluble wax together with an organopolysiloxane as the effective component of the defoaming agent followed by solidification by cooling and therefore would appear to solve the above problems.
However, considering this known solid silicone defoaming agent, it is noted that the miscibility of the organopolysiloxane with the water-soluble wax is poor, which causes the appearance of a heterogeneous phase upon solidification from the melt during production. Due to this heterogeneous phase, the solid defoaming agent will not satisfactorily disperse in water when it is applied, and a portion remains undissolved.
Attempts have been made to solve this problem by the addition of an emulsifying agent. However, the defoaming effect is significantly weakened when a large quantity of hydrophilic emulsifying agent is added. Another problem is encountered when a lipophilic emulsifying agent is added, that is, the organopolysiloxane component becomes less dispersible in water, with the result that a satisfactory defoaming effect is not realized.
Japanese Kokai Patent Application No. 59-222209 [222,209/84] discloses a solid defoaming agent which includes a polyoxyethylene group-containing water-soluble wax in a silicone oil compound. However, while the dispersibility of the silicone oil compound in water is improved with this solid defoaming agent, the properties nevertheless remain unsatisfactory. Furthermore, a high-shear dispersion device is required in the preparation of the solid defoaming agent in order to obtain a homogeneous composition. An additional disadvantage is that a quenching process is required.